Question

假设以下代码

private readonly T entity;

public bool HasUnique<T>(Expression<Func<T, object>> property, IEnumerable<T> entities)
{
}

property是T实体的属性表达式。

如何检查entities中是否有与[{1}}具有相同属性值的元素，而属性是从给定的属性表达式解析的？

到现在为止，我可以从实体

获取属性名称及其值

问题似乎是如何在运行时设置并执行谓词？像

这样的东西

entity

用法就像这样

Func<T, bool> predicate = // build a predicate
var isUnique = !entities.Any(predicate);

Answer 1

我试图找出单词＆＃34; Unique＆＃34;与您描述的内容有关，并且您的示例用法并不涉及任何实体来比较people的内容，但我认为您正在寻找类似的内容？

public static bool HasUnique<T>(this T referenceItem, Func<T, object> property, 
                                IEnumerable<T> entities)
{
    var referenceProperty = property(referenceItem);
    return entities.Any(e => property(e) == referenceProperty);
}

或者这个：

public static bool HasUnique<T>(this T referenceItem, Func<T, object> property, 
                                IEnumerable<T> entities)
{
    var referenceProperty = property(referenceItem);
    return entities.Any(e => property(e).Equals(referenceProperty));
}

甚至这个：

public static bool HasUnique<T, TProp>(this T referenceItem, Func<T, TProp> property, 
                                IEnumerable<T> entities)
{
    var referenceProperty = property(referenceItem);
    return entities.Any(e => property(e).Equals(referenceProperty));
}

Answer 2

您需要Expression<Func<T,object>>吗？因为只需Func<T,object>即可实现。

using System;
using System.Collections.Generic;
using System.Linq;

namespace LinqPlayground
{
    class Program
    {
        public class UniqueChecker<T>
        {
            public bool HasUnique<T>(Func<T, object> property, IEnumerable<T> entities)
            {
                var uniqueDict = new Dictionary<object, bool>();
                foreach (var entity1 in entities)
                {
                    var key = property(entity1);
                    if (uniqueDict.ContainsKey(key))
                    {
                        uniqueDict[key] = false;
                    }
                    else
                    {
                        uniqueDict.Add(key, true);
                    }
                }
                return uniqueDict.Values.All(b => b);
            }
        }

        public class Person
        {
            public string Name { get; set; }
        }

        static void Main(string[] args)
        {
            var people = new List<Person>
            {
                new Person {Name = "Chris"},
                new Person {Name = "Janet"},
                new Person {Name = "John"},
                new Person {Name = "Janet"},
            };

            var checker = new UniqueChecker<Person>();


            Console.WriteLine("Are names unique? {0}",checker.HasUnique(person => person.Name, people));
        }
    }
}

使用Expression <func <t，object =“”>＆gt; </func <t，>中的信息创建运行时谓词

2 个答案: